Duration of Contagion of Foot-And-Mouth Disease Virus in Infected Live Pigs and Carcasses.

Carolina Stenfeldt,Amy H Delgado,Miranda R Bertram,Jonathan Arzt,George R Smoliga,Ethan J Hartwig

doi:10.3389/fvets.2020.00334

Abstract

Data-driven modeling of incursions of high-consequence, transboundary pathogens of animals is a critical component of veterinary preparedness. However, simplifying assumptions and excessive use of proxy measures to compensate for gaps in available data may compromise modeled outcomes. The current investigation was prospectively designed to address two major gaps in current knowledge of foot-and-mouth disease virus (FMDV) pathogenesis in pigs: the end (duration) of the infectious period and the viability of FMDV in decaying carcasses. By serial exposure of sentinel groups of pigs to the same group of donor pigs infected by FMDV A24 Cruzeiro, it was demonstrated that infected pigs transmitted disease at 10 days post infection (dpi), but not at 15 dpi. Assuming a latent period of 1 day, this would result in a conservative estimate of an infectious duration of 9 days, which is considerably longer than suggested by a previous report from an experiment performed in cattle. Airborne contagion was diminished within two days of removal of infected pigs from isolation rooms. FMDV in muscle was inactivated within 7 days in carcasses stored at 4oC. By contrast, FMDV infectivity in vesicle epithelium harvested from intact carcasses stored under similar conditions remained remarkably high until the study termination at 11 weeks post mortem. The output from this study consists of experimentally determined data on contagion associated with FMDV-infected pigs. This information may be utilized to update parameterization of models used for foot-and-mouth disease outbreak simulations involving areas of substantial pig production.

Highlights

Foot-and-mouth disease (FMD) is a high-impact viral disease capable of infecting all cloven-hoofed domestic livestock and numerous wildlife species [1]
Vesicular lesions appeared at 2–3 dpi, and all pigs were viremic and shedding high quantities of foot-and-mouth disease virus (FMDV) RNA (6.15–8.25 log10 genome copy numbers (GCN)/ml) by the first sampling time point at 2 dpi (Figure 1, Table 1)
The range of FMDV RNA detected in oropharyngeal fluid (OPF) from the donor pigs at 5 dpi was 6.12–7.08 log10 GCN/ml

Summary

Introduction

Foot-and-mouth disease (FMD) is a high-impact viral disease capable of infecting all cloven-hoofed domestic livestock and numerous wildlife species [1]. The causative agent, foot-and-mouth disease virus (FMDV; genus: Aphthovirus, family: Picornaviridae) causes initial infection via the upper respiratory- or gastrointestinal tracts (depending on host species), followed by systemic generalization with lameness, inappentence, and vesicular lesions on the feet and in the mouth as characteristic clinical findings [2, 3]. Due to the potentially catastrophic consequences associated with incursions of FMDV into previously free countries [5], substantial efforts are invested into veterinary preparedness and contingency planning. Such endeavors often include mathematical modeling of FMD outbreaks within defined geographic regions for the purpose of estimating disease spread and impact, and to evaluate the effect of applied control measures [6]. Essential input parameters need to reflect the detailed structure of the susceptible population, as well as intrinsic factors of host-pathogen interactions that capture the progression of infection and contagiousness within individual animals

Methods

Results

Discussion

Conclusion